1. Field of the Invention
The present invention relates to a method of preparing a negative-electrode active material of a lithium secondary battery, and more particularly to a method of preparing a silicon oxide (SiOx)-carbon composite as a negative-electrode active material of a lithium secondary battery.
2. Description of the Related Art
Secondary batteries are being used as large power storage batteries for electric vehicles or battery power storage systems and small high-performance energy sources for portable electronic devices such as mobile phones, camcorders, notebooks, etc. In order to reduce the size of portable electronic devices and attain long-term continuous use thereof, secondary batteries able not only to achieve lightness of parts and low power consumption but also to ensure high capacity despite being small are required.
Recently, in the market related to secondary batteries, the development of a negative-electrode active material which enables a large size, high capacity and high performance has become essential, in order to serve in portable electronic devices and information communication devices, and also in energy storage devices for hybrid vehicles (HEV or PHEV) or power generation systems.
However, a highly crystalline carbon-based active material that is commercially available as a negative-electrode active material for a conventional secondary battery has a limited theoretical capacity of 372 mAh/g despite having superior characteristics as active materials for batteries. Hence, the development of a non-carbon-based negative-electrode active material is essential to manufacture high-capacity and high-performance lithium secondary batteries.
In the non-carbon-based negative-electrode active material, silicon (Si) has a high discharge capacity of 4,200 mAh/g and a very low lithium reaction potential of 0.4 V (Li/Li+), and is thus known to be the most appropriate for a negative-electrode material.
However, silicon is problematic because volume expansion takes place at up to 400% at a maximum upon insertion (charge) of lithium ions, and thus the capacity is not maintained, and also because of low electrical conductivity or the like, and thereby it is necessary to solve the above problems before silicon can be commercialized as a negative-electrode active material.